Light emitting diodes (LEDs) for use as indicators are well known. LEDs have been used extensively for this purpose in consumer electronics. For example, red LEDs are commonly used to indicate that power has been applied to devices such as radios, televisions, video recorder (VCRs) and the like.
Recently, high-power LEDs have seen increased use in general lighting applications. For example, high-power LEDs can now be found in overhead lighting, street lighting, and in automotive application, such as in automobile headlamps. Typically, high-power LEDs are provided as an assembly comprising one or more LEDs mounted to a substrate and protected by an encapsulation. Light emitted from the LEDs passes through and is focused by the encapsulation before it is visible to a user.
It is desirable to have high-power LED assemblies that produce light of different colors. For example, white light can be produced by using phosphor to convert blue light emitted from an LED. In conventional LED assemblies, an organic phosphor dye is use to coat the LED chip. Unfortunately, this arrangement has poor conversion efficiency and low light output because of “backscatter.” Backscatter occurs because the phosphor layer is in direct contact with the LED chip causing light to reflect back toward the LED chip thereby decreasing light output.
Therefore, what is needed is a way to avoid the problems associated with backscatter to increase the optical output of high power LEDs